1. Field of the Invention
The present invention relates to an image forming apparatus capable of counting a consumable consumption amount, and a control method and a control program therefor, and more particularly, to an image forming apparatus, control method, and control program that measure a consumption amount of a consumable material used in the image forming process.
2. Description of the Related Art
In electrophotographic and electrostatic image forming apparatuses in general, the toner density of a two-component developing agent comprised of a carrier and a toner, that is, the ratio of the weight of the toner particles to the total weight of the carrier particles and toner particles, is an extremely important factor in stabilizing the quality of images. During development, of the developing agent only the toner particles are consumed whereas the carrier particles are not consumed, and therefore the toner density decreases as the developing process proceeds. As a result, it is necessary to use a toner density controller (that is, an ATR, or Automatic Toner Replenisher) in order to accurately detect developing agent toner density and to replenish toner particles depending on the decrease in toner density as suitable, so as to continuously maintain the toner density at a constant level and thus maintain the quality of images.
Conventionally, devices employing a variety of methods have been implemented, such as toner density detection devices and toner density control devices that correct changes in toner density inside a developing device.
Such methods include a method of detecting the toner density from the reflectance of the developing agent when light is irradiated onto either the developing agent conveyed by the developing device to a development sleeve or the developing agent inside a developing agent container of the developing device, a permeability detecting method, and a method of controlling the toner density indirectly from a patch image density.
However, the method of detecting the toner density from the reflectance of the developing agent suffers from a problem that it becomes impossible to accurately detect the toner density if a photosensor used to detect the toner density has become soiled by toner spatter or the like.
Moreover, the ATR employing the permeability detecting method suffers from a problem that a sensor output signal corresponding to the apparent permeability (inductance) changes discontinuously, and it becomes impossible to accurately detect the toner density if there is a change in the apparent density of the developing agent due to neglect of the developing agent or there are environment changes between just before stopping operation of the image forming apparatus and just after restarting operation of the image forming apparatus.
Moreover, the method of controlling toner density indirectly from a patch image density has the disadvantage that, as image forming apparatuses have become more compact, it has become impossible to secure either the space needed to install a patch density sensor inside the image forming apparatus or the space needed to form the patch image on the development sleeve.
To solve the problems described above, a toner replenishment method using a video count process has been implemented (see Japanese Laid-Open Patent Publication (Kokai) No. H05-323791).
According to this toner replenishment method, the video count process is performed in which the output level of each pixel of a digital image signal (image density signal) is converted into a signal indicative of a toner consumption amount and these toner consumption amount signals are counted and accumulated (the accumulated value will be referred to as “the video count value”). After the video count process, the amount of toner to be consumed is calculated from a print level ratio of the output image to thereby replenish the developing agent container with toner as appropriate. In other words, the video count value is converted into a toner replenishment amount and toner in that replenishment amount is supplied to the developing agent container, thus maintaining the toner density inside the developing agent container, which decreases with development, at a constant level.
On the other hand, Multi Function Printers (MFPs) equipped with copier, facsimile and printer capabilities have become widely used. Typically, such MFPs are comprised of a controller, which performs image processing based on input data from an external source, and an engine, which includes an engine controller that performs image formation processing (that is, recording by a recording section) based on image-processed data supplied from the controller.
The controllers of such MFPs have become very sophisticated. Moreover, to reduce the cost of the engine or for some other reason, such controllers are sometimes equipped with image processors that perform a variety of types of image processing.
Moreover, the controller is sometimes equipped with hardware dedicated to a specific process. For example, to transfer image data to the engine, a typical controller is provided with hardware employing DMA (Direct Memory Access) transfer, which is capable of high-speed processing.
Further, it can be envisaged that the controller will eventually be configured so as to perform a video count of image data that is transferred to the engine.
However, having the controller perform the video count process involves several problems.
For example, image data continues to be transferred even if the image forming process performed by the engine stops in the middle of a page, and therefore incorrect consumption count of the consumable material, i.e. the developing agent is performed based on the video count value of the transferred image data despite the fact that no consumable material has been consumed because image forming means including the engine has stopped.
Further, for example, if the controller has been interrupted a requested image transfer process by the DMA transfer due to the occurrence of a malfunction such as a jam, an exclusive process or a failsafe process for determining at what timing the DMA transfer been interrupted and from where the recovery is to be started is performed. To prevent such exclusive process or failsafe process from being performed, it is necessary to make the software more complicated, but doing so increases the probability of bugs arising and decreases the performance of the overall system.
Further, even where the DMA transfer is not used, if a printing process is performed in synchronism with a scanning process, the image transfer cannot be stopped midway and the same problems as described above arise.